1. Field of the Invention
The invention concerns a process for the dyeing of non-woven textile fabrics. More particularly, the invention relates to the dyeing of tufted pile fabrics by a process including placement of the non-woven fabric into a dye solution mixed with foaming chemicals followed by treatment with saturated steam.
2. Background of the Art
In the dyeing of textile pile fabric, particularly tufted carpets, it is of decisive importance to obtain a uniform wetting of the pile and to maintain a uniformity of wetting during the entire dyeing process. Without uniform wetting, uniform dyeing of the fabric cannot be assured. An inadequate penetration of the dyeing solution in depth in the fabric leaves the pile without exposure to the dye in its base area, while possibly overdyeing the peak areas. On the other hand, the introduction of an insufficient amount of the dye particularly in the steam phase will result in the bleaching of peaks.
In the known dyeing processes for the abovedescribed reasons, the non-woven textile fabric is soaked to saturation with the dyeing solution. The amount of dyeing solution necessary for saturation depends on the structure of the pile fabric itself with an amount of the dyeing solution being at least 300% to 700% with respect to the weight of the dry material to be dyed. After saturation with the dyeing solution, the fabric is filled and thereafter immediately placed in the steaming apparatus. The boiling bubbles generated during the treatment with saturated steam (and supported by the foaming agents contained in the dyeing solution) cause the solution to foam and thus to penetrate the fabric. This generally results in a uniform dyeing of the pile over its entire height. The results of dyeing with this process are generally satisfactory, but the necessary quantity of the dyeing solution amounting to several times the weight of the fabric to be dyed is considered to be disadvantageous because it requires the consumption of extraordinarily high quantities of energy for both the heating to a boiling temperature and the subsequent drying of the pile fabric. Furthermore, in spite of the use of large amounts of the dyeing solution, quality defects, especially in the form of longitudinal streaking, cannot be completely prevented.
To reduce the high energy requirements of the described saturation-steaming process, the so-called form dyeing process has come into use more recently. According to the foam dyeing process, the dyeing solution is mixed with foaming agents and prefoamed by means of mechanical stirring. The foam product in this manner is applied to the material to be dyed in a layer thickness of 10-20 mm and suctioned into the pile fabric by the application of suction to the backside of the fabric. The pile fabric is then exposed in the usual manner to a treatment with steam. According to this known process, the amount of the dyeing solution necessary may be reduced to 200%, with a corresponding reduction in the energy required for the subsequent steaming and drying process. However, the problems arising from the maintenance of a uniform color quality are thereby enhanced. It has been found that the quality of the color depends decisively on the degree of foaming of the dyeing solution, i.e., on the ratio of liquid to air in the foam. The maintenance of a narrow ratio of liquid to air is necessary but difficult. This ratio within the narrow range cannot be insured over extended periods of time. The use of this process, therefore, constantly results in inadequate dye-through or in dark areas because of overdyeing. Problems arise from the fact that the foam particles are not suctioned into the fabric, and they break down during the steaming process only where they cause excessive pigmentation of the pile fabric in the peak areas.